Abstract
The flood‐dry‐flood cycle in the reservoir riparian zone (RRZ) of the Three Gorges Dam has dramatically altered the riparian ecosystem structure and composition. Previous field studies have shown that leaf traits varied greatly and were restricted to the lower‐investment and faster‐return end of the global leaf spectrum, which are typical characteristics of fast‐growing species. However, it is unclear as to the mechanism underpinning the growth potential of these species and how it will respond to soil nutrient availability and temperature. Here, we linked the plant functional traits of four representative dominant C4 herbaceous species (Setaria viridis, Echinochloa crusgalli, Cynodon dactylon and Hemarthria altissima) to their relative growth rates (RGR) under ambient and elevated temperatures, with different nitrogen and phosphorus levels, to explore the potential mechanism of species growth in the newly established reservoir riparian ecosystem in the Three Gorges Reservoir Area, China. We grew seedlings of these species in four open‐top chambers, with three levels of nutrient supplies under two temperature gradients (ambient temperature and an elevated temperature of 4°C). We found that the responses of the RGR and plant traits to soil N and P supply levels and temperature varied considerably among studied species. E. crusgalli displayed the lowest RGR associated with relatively low specific leaf area (SLA), leaf nitrogen content (LN), stem mass ratio (SMR), and high leaf mass ratio (LMR) and was less affected by soil N and P supply levels and temperature. C. dactylon and H. altissima showed the highest RGR compared to the other two species grown at the substrate of N = 0.4 mg/g, P = 0.2 mg/g at ambient air temperature, associated with a relatively high SMR, low LMR and low plant carbon content (PCC). However, the RGR advantage of the two species was diminished at elevated temperatures, while S. viridis showed the highest RGR compared to the other species. Across all datasets, the RGR had no association with the leaf area ratio (LAR) and SLA. The RGR also showed no significant relationships with the LN and leaf phosphorus content (LP). On the other hand, the RGR was captured adequately by the SMR, which can therefore be considered as a powerful functional marker of species’ functioning in this newly established reservoir riparian ecosystem. Our study provides some insight into the underlying mechanisms of species growth in reservoir riparian ecosystems.
Highlights
The Three Gorges Dam (TGD) is the largest dam in China (Wu et al, 2004)
Along a flooding gradient in the riparian zone of the Three Gorge Reservoir Area (TGRA), field studies showed the dominance of C. dactylon and H. altissima gradually decreased, while S. viridis increased from lowlands to highlands, after several years’ impoundment (Li et al, 2015; Liu, Wang, Wang, & Yang, 2012; Wang et al, 2012; Ye et al, 2013). In line with these findings, the results in the present study demonstrated that at the ambient air temperature, the relative growth rates (RGR) of C. dactylon and H. altissima gradually decreased from lowlands (N = 0.4 mg/g, P = 0.2 mg/g) to highlands (N = 1 mg/g, P = 0.1 mg/g), and there was a trend that S. viridis had a higher RGR in highlands (Figure 2)
To the best of our knowledge, this is the first study to investigate the response of the RGR to soil nutrient availability and temperature in a newly established reservoir riparian ecosystem in China
Summary
The Three Gorges Dam (TGD) is the largest dam in China (Wu et al, 2004). Water levels in the reservoir vary from 175 m above sea level (a.s.l.) in winter to 145 m a.s.l. in summer, with a short exposure time of an average of 130 days per year at 158 m a.s.l. (Fan, Xiong, Zhang, Liu, & Xie, 2015). There is a large body of the literature on the physiological consequences experienced by riparian species due to tremendous water-level fluctuations in the TGRA (Lei, Zeng, Xu, & Zhang, 2017; Li et al, 2011, 2015; Lu, Li, Jiang, Huang, & Bao, 2010), the responses of RGR to environmental variables, and the functional coordination between plant traits and the RGR in the newly established ecosystem,. S. viridis and E. crusgalli are annuals, while C. dactylon and H. altissima are perennials These four herbaceous species co-occurred and were predominant at different sites in the riparian zone formed by the TGRA in China (Wang et al, 2012; Zhang et al, 2016). We aimed to: (1) determine how the RGR responds to soil nutrient status and temperature and whether it be applied to explain the species distribution pattern in the riparian ecosystem in TGRA, and (2) determine which plant functional traits explained the most variation in the RGR
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